1. Field of the Invention
The present invention relates generally to an automatic transmission and more specifically to a control system for such a device.
2. Description of the Prior Art
U.S. Pat. No. 4,730,521 issued on Mar. 15, 1988 discloses an automatic automotive transmission which can produce four forward speeds and one reverse.
In this transmission a one-way clutch and a forward clutch are directly aligned and an overrunning clutch is arranged in parallel with the one way clutch and the forward clutch. The forward clutch is engaged in all forward gears (viz., engaged in first, second, third and fourth gears). The one-way clutch is engaged during first, second and third forward speeds and un-engaged during fourth speed.
When the transmission is conditioned for D range the overrunning clutch is not engaged however it is engaged when engine braking is required and the transmission is selectively conditioned to produce one of first, second and third gears. Accordingly, when the transmission is set in D range rotational energy is transmitted via the forward and one-way clutches. With this arrangement the shift timing between third and fourth gears is easily adjusted.
However, this arrangement has suffered from the drawback that, especially when the engine throttle valve is fully closed and an upshift such as a 1-2. 1-3 or a 2-3 upshift takes place, an undesirable knocking noise is produced in the one-way clutch.
The reason for this is that, when these shifts take place the engine rotational speed is reducing and at the same time the torque applied to the one-way clutch disappears. This momentarily permits the one-way clutch to assume an un-engaged condition. Following this the engine speed decreases until it matches the newly established transmission conditions. However, at this time torque is momentarily applied to the one-way clutch (see peak P in FIG. 5B) whereafter a coasting condition is established. This induces the one-way clutch to again assume an unengaged state.
As there is a small amount of relative movement possible between the races of the one-way clutch, the sudden re-application of torque to the device causes a sudden amount of movement, such as shown at K in FIG. 5C, and the knocking produced when the two elements engage at the end of the movement.
Apart from producing undesirable noise, this also deteriorates the shift feeling produced by the transmission and additionally detracts from the operational characteristics of the arrangement.